This investigation is designed to optimize the use of the neodymium:YAG laser in liquefying the vitreous. The resultant release of vitreous traction will improve the management of many diseases, including cystoid macular edema, macular breaks, preretinal fibrosis, and proliferative diabetic retinopathy. The specific aims are: (1) to demonstrate that the neodymium:YAG laser may be helpful in liquefying the vitreous, (2) to build an optical device that will increase the safety and efficience of applying neodymium:YAG laser energy in the vitreous, and (3) to determine the safest and most efficient parameters of the YAG laser. The methodology includes use of (a) the M-Tec 2000 neodymium:YAG laser (Medical Laser), which uses the M-mode and can deliver energy up to 5 mJ, (b) the system 9900 neodymium:YAG laser (Coherent), which uses the Q-switched mode and can deliver energy up to 11 mJ, (c) the optical device (Aim 2) that will allow application of laser energy in the vitreous while focusing on the retina, giving a fixed, identifiable target, (d) a formula that allows computation of the distance between the retina and the application, (e) the El Bayadi-Kajiura (EBK) preset aspheric lens for in vivo evaluation of vitreous consistency, and (f) rabbits. Experiment I: To demonstrate that neodymium:YAG laser energy applied to the vitreous causes its liquefaction. Vitreous changes produced by 10,000 neodymium:YAG laser burns will be documented with the EBK lens and with Foos's suspension-in-air technique. Treated and untreated eyes will be compared. Experiment II: To determine the safe distance at which YAG laser burns of various energy levels can be applied in the vitreous. Burns will be placed at different distances from the retina, and the shortest distance at which no retinal damage occurs will be determined. Experiment III: To determine the minimum number of YAG laser burns of various energy levels needed to produce vitreous liquefaction. 1000 applications will be given at a time. A vitreous study using the EBK lens will be performed after each 1000 applications. Sets of 1000 burns will be given until vitreous liquefaction can be documented. Liquefaction will be confirmed by pathologic examination.